Many chemical process streams are operated under sterile conditions; i.e., wherein there is essentially no contamination by microorganisms. However, sterile process streams are often monitored by withdrawing samples of process fluids from those streams. Productivity and product quality can diminish if the process streams are contaminated during sampling.
A common method of withdrawing samples from a sterile process stream includes partitioning the process stream from the environment by a septum. A syringe needle is employed to perforate the septum and to remove a sample from the process stream. Removal of the needle from the septum reseals the process stream. A portion of the withdrawn sample, however, can be trapped within the perforation created by the needle. Reintroduction of the needle at or near a perforation containing remnants of a previous sample can disturb these remnants and cause their reentry into the sterile process stream, thus contaminating otherwise sterile conditions. Septums are also damaged by perforation and can require replacement during processing. Further, pressure within process streams can cause process fluid to leak through perforations in septums, thereby contaminating the septum and the environment.
Conventional valves often trap sample material when they are closed. For example, diaphragm valves typically are closed by directing a diaphragm against an interior surface of the valve. Sample material can become trapped between the diaphragm and the interior surface. Ball valves, as another example, usually include a spherical member having a conduit therethrough which conducts fluid from a process stream when the valve is open. The spherical member is rotated to close the valve, thereby creating a dead space which traps sample material within the conduit. Trapped material within either a diaphragm valve or a ball valve generally cannot be removed without reopening the valve. In addition, a sample side of conventional valves can usually be flushed when the valve is closed only by directing a fluid into the sample side in a direction of flow countercurrent to that of sample flow when the valve is open. Also, fluid is often flushed through separate ports in valves to attempt to sterilize areas where process material has been trapped. This flushing generally is inadequate to remove remnants of previous samples from the sample side of valves.
Thus, a need exists for a new apparatus and method for sampling sterile process streams which minimize or overcome the above-mentioned problems.